The invention relates to a hybrid vehicle comprising a drive train which has two electric machines, wherein both serve to drive the vehicle on one drive axle each, which drive axles are not mechanically coupled to one another, is known as the vehicle RX450h from Lexus. The electrical loads of the vehicle are connected to energy sources via an on-board electrical system. Vehicles with an electric traction drive have a high-voltage on-board electrical system for supplying the electric drive and further high-voltage loads. The high-voltage on-board electrical system is connected to a low-voltage on-board electrical system which serves to supply the low-voltage loads of the vehicle.
It is known to operate one of the electric machines of a hybrid vehicle at certain times in a generator mode in order to generate electrical energy to supply the loads and to charge the energy accumulators. When high-power loads, for example an electrically operated vehicle air-conditioning system, are switched on, on the one hand electrical power peaks are produced, and therefore voltage dips in the on-board electrical system of the vehicle, and on the other hand the rotational speed of the drive train and of the electric machine which is operated in a generator mode collapses since the internal combustion engine does not output within a very short time a significantly increased torque which is necessary for this purpose. When the loads are switched off, voltage peaks and rotational speed overshoots correspondingly occur in the drive train.
In order to reduce this electrical loading of the on-board electrical system and the undesired fluctuations in rotation speed in the drive train during the operation of the hybrid vehicle, different measures are known for stabilizing the voltage, for example buffering energy in the on-board electrical system by means of capacitors.